Studies mapping the cortical representation of the muscles on the two sides of the larynx in each hemisphere in normal volunteers using transcranial magnetic stimulation have continued. Muscles on the left and right sides can be stimulated by cortical stimulation in either hemisphere. In some normal volunteers, the area of representation of the laryngeal muscles was greater in the left than in the right hemisphere. Studies aimed at examining brain activation patterns in normal volunteers during speech and voice activities using Positron Emission Tomography are continuing. Our aim is to determine the degree to which different voice, speech and language tasks are dominant in the left hemisphere. The H215O technique is being used to estimate blood flow over very brief periods of time, approximately 40 seconds. Eight studies are being conducted in one session with a subject, to compare activation patterns across tasks. Statistical Parametric Mapping has been used for initial analysis of a small group of normal right handed controls and right handed stutterers. In the controls, during humming and oral-lingual non-speech movements, a slight left hemisphere predominance has been found in the inferior rolandic cortex and the superior temporal (Heschl's) gyrus over rest. Activation during humming and oral- lingual movements, when compared with gibberish or nonsense speech, demonstrated somewhat greater activity on the left in the antero-Rolandic area. Marked right-left hemispheric differences, however, were only noted during language based tasks such as expository speech or sentence construction. Normal controls' predominantly left hemisphere brain activation during speech involving language was not been seen in preliminary analyses of chronic adult stutterers. Additional fluent and non- fluent subjects are being tested to determine if more detailed analyses will continue to support these trends.